Low-power pulse width encoding scheme and counter-less shift register that may be employed therewith

ABSTRACT

A method of decoding an encoded signal includes steps of receiving the encoded signal, creating a decoding signal by delaying the encoded signal by a predetermined amount of time Δ, sampling the encoded signal using the decoding signal, and determining a value of each of a plurality of decoded bits represented by the encoded signal based on the sampling. Also, a method of operating a shift register wherein the shift register has an initialization state wherein a first binary symbol is stored in a first position and a second binary symbol different than the first binary symbol is stored in each of one or more intermediate positions and a last position. The method includes determining that the shift register is full responsive to detecting that the first binary symbol has been stored in either one of the intermediate positions or the last position.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.13/568,663, entitled “Low-power Pulse Width Encoding Scheme andCounter-Less Shift Register That May Be Employed Therewith” and filed onAug. 7, 2012, which claims priority under 35 U.S.C. §119(e) fromprovisional U.S. patent application No. 61/522,072, filed Aug. 10, 2011,the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to data encoding schemes, and inparticular, to a data encoding scheme and associated decoding method anddevice that does not employ a digital clock or system clock signal. Thepresent invention also pertains to a counter-less shift register thatmay be employed in connection with the data encoding scheme of thepresent invention.

2. Description of the Related Art

In a wireless serial data transmission system, a data stream in the formof a series of binary symbols (e.g., 1s and 0s) is typically transmittedfrom a transmitter device to a receiver device by: (i) encoding the datastream and thereby generating an encoded data signal (by converting theseries of binary symbols to an analog form according to an encodingscheme), (ii) transmitting the encoded data signal from the transmitterdevice to the receiver using an appropriate modulation technique, (iii)receiving and demodulating the transmitted signal at the receiver devicein order to obtain the original encoded data signal, and (iv) decodingthe encoded data signal in the receiver device to extract/obtain theoriginal data stream (the series of binary symbols) from the encodedsignal. In current data transmission methods, the receiving deviceextracts/obtains the original data stream from the encoded signal usingan explicit clock signal that is common to the transmitter device andthe receiver device. The explicit clock signal is either separatelygenerated using additional dock circuitry provided as part of thereceiver device or extracted from the transmitted data.

For example, one type of prior art encoding technique is known as pulsewidth coding (PWC) or pulse interval encoding (PIE). In PWC and PIE,each bit of data/binary symbol (e.g., each 1 and 0) is represented by anenergy pulse having a certain duration. For instance, a 1 may berepresented by a pulse having a width equal to 5 clock pulses and a 0may be represented by a pulse having a width equal to 3 clock pulses.Thus, determining the number of clock pulses within each received energypulse enables that energy pulse to be decoded as either a binary 1 or abinary 0. FIG. 1 is a schematic diagram representing such a PWC or PIEscheme. As will be appreciated, such a scheme requires a local, highfrequency clock signal at the receiver device, which in turn leads to ahigh power requirement at the receiver device.

As another example, in Manchester encoding, the clock signal is providedwithin the code itself, allowing the clock to be extracted at thereceiving end by sampling the received signal and counting the number ofsamples within each symbol received. This means that there must be aclock present at the receiver device that provides a sampling signal ata higher bit rate than the incoming data stream, which in turn leads toa high power requirement at the receiver device.

Power consumption is a major concern in many electronic systems. Forexample, power consumption is a major concern in UHF passive RFID tagsystems, wherein the operating range of such systems mainly depends onthe power consumption of the RFID tags. Many current UHF passive RFD tagsystems employ PIE, wherein the tag includes a PIE decoder module. ThePIE decoder module in known to consume a significant amount of power dueto the fact, as described above, it uses a high frequency oscillator todetermine the width of each portion of the encoded signal in order todistinguish a 1 bit from a 0 bit.

There is thus a need for an encoding scheme and associated decodermodule that eliminates the use of a high power consuming clock (e.g., ahigh frequency clock), thereby lower power consumption at the receivingend.

SUMMARY OF THE INVENTION

In one embodiment, a method of decoding an encoded signal is providedthat includes steps of receiving the encoded signal, creating a decodingsignal by delaying the encoded signal by a predetermined amount of timeΔ, sampling the encoded signal using the decoding signal, anddetermining a value of each of a plurality of decoded bits representedby the encoded signal based on the sampling.

In another embodiment, a decoder circuit for decoding an encoded signalis provided that includes means for creating a decoding signal bydelaying the encoded signal by a predetermined amount of time Δ, andmeans for sampling the encoded signal using the decoding signal anddetermining a value of each of a plurality of decoded bits representedby the encoded signal based on the sampling.

In still another embodiment, a method of encoding a data signalincluding a plurality of first symbols and a plurality of second symbolsis provided that includes creating an encoded signal based on the datasignal, wherein in the encoded signal each of the first symbols isrepresented by a first square wave having a first period P₀ and a firstduty cycle D₀ and each of the second symbols is represented by a secondsquare wave having a second period P₁ and a second duty cycle. D₁, andwherein D₁>D₀ and P₁≧P₀.

In yet another embodiment, a method of operating a shift register havingn sequentially arranged storage positions comprising a first position, alast position and one or more intermediate positions between the firstposition and the last position is provided, wherein a bit array storedby the shift register will shift by one position each time that at newbit is loaded into the first position. The method includes causing theshift register to be in an initialization state wherein a first binarysymbol is stored in the first position and a second binary symboldifferent than the first binary symbol is stored in each of the one ormore intermediate positions and the last position, and determining thatthe shift register is full responsive to detecting that the first binarysymbol has been stored in either one of the intermediate positions orthe last position.

These and other objects, features, and characteristics of the presentinvention, as well as the methods of operation and functions of therelated elements of structure and the combination of parts and economiesof manufacture, will become more apparent upon consideration of thefollowing description and the appended claims with reference to theaccompanying drawings, all of which form a part of this specification,wherein like reference numerals designate corresponding parts in thevarious figures. It is to be expressly understood, however, that thedrawings are for the purpose of illustration and description only andare not intended as a definition of the limits of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram representing a prior art PWC or PIEscheme;

FIG. 2 is a schematic diagram representing a low-power pulse widthcoding scheme according to an exemplary embodiment of the presentinvention;

FIG. 3 is a schematic diagram representing how a signal encoded usingthe scheme of FIG. 2 may be decoded according to an embodiment of thepresent invention;

FIG. 4 is a schematic diagram of a decoder circuit according to anexemplary embodiment of the present invention;

FIGS. 5A-7B are schematic diagram representing operation of acounter-less shift register according to various exemplary embodiments;

FIG. 8 is a schematic diagram of an RFID system according to anexemplary embodiment of the present invention; and

FIG. 9 is a schematic diagram of showing portions of an RFID tag formingpart of the RFID system of FIG. 8.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

As used herein, the singular form of “a”, “an”, and “the” include pluralreferences unless the context clearly dictates otherwise. As usedherein, the statement that two or more parts or components are “coupled”shall mean that the parts are joined or operate together either directlyor indirectly, i.e., through one or more intermediate parts orcomponents, so long as a link occurs. As used herein, “directly coupled”means that two elements are directly in contact with each other. As usedherein, “fixedly coupled” or “fixed” means that two components arecoupled so as to move as one while maintaining a constant orientationrelative to each other.

As used herein, the word “unitary” means a component is created as asingle piece or unit. That is, a component that includes pieces that arecreated separately and then coupled together as a unit is not a“unitary” component or body. As employed herein, the statement that twoor more parts or components “engage” one another shall mean that theparts exert a force against one another either directly or through oneor more intermediate parts or components. As employed herein, the term“number” shall mean one or an integer greater than one (i.e., aplurality).

Directional phrases used herein, such as, for example and withoutlimitation, top, bottom, left, right, upper, lower, front, hack, andderivatives thereof, relate to the orientation of the elements shown inthe drawings and are not limiting upon the claims unless expresslyrecited therein.

In one aspect, the present invention provides a low-power pulse widthcoding scheme and associated decoding method and apparatus wherein adecoding mechanism is created from the encoded signal and is used todecode the encoded signal. This enables the decoding to be performedwithout the need for a high frequency clock signal, and thus reduces thepower consumption of the decoder unit. In particular, as described indetail below, the decoding mechanism is created from the encoded signalby creating a decoding signal by delaying the encoded signal, preferablyusing only passive components in the form of a delay line or buffer orsimilar element. That decoding signal is then used to sample the encodedsignal in order to decode the encoded signal. Thus, the low-power pulsewidth coding scheme of the present invention is an auto correlatingscheme that reduces power consumption wherein the original encodedsignal provides the decoding mechanism for the scheme.

The pulse width coding scheme of the present invention will now bedescribed with reference to FIG. 2 in connection with an exemplaryembodiment thereof. As seen in FIG. 2, in the low-power pulse widthcoding scheme of the exemplary embodiment, the binary symbol “0” isrepresented by a square wave having a period P₀ and a duty cycle D₀ andthe binary symbol “1” is represented by a square wave having a period P₁and a duty cycle D₁. As used herein, the term “square wave” shall mean asignal that begins at a first level (e.g., logic high) and then at somepoint within the square wave, switches from the first level to the asecond level (e.g., logic low) different than the first level for theduration of the square wave (i.e., for the duration of the signalperiod). As used herein, the term “period” shall mean the amount of timein a square wave measured from the beginning of the first level to theend of the second level, and shall define one full cycle of the squarewave. As used herein, the term “duty cycle” shall mean the amount oftime in a square wave wherein the signal has a particular, predeterminedone of the two levels therein, i.e., the first level or the secondlevel, depending on the implementation. Thus, in FIG. 2, the waveformpresented represents an example 8-bit input symbol data stream“01011010” in the present encoding scheme.

In addition, according to an aspect of the pulse width coding scheme ofthe present invention, D₀<<D₁ and P₀≦P₁. In other words, the duty cycleD₁ must be at least a predetermined amount greater than the duty cycleD₀, and the period P₁ must be greater than or equal to the period P₀.The predetermined amount by which D1 must be greater than D₀ will bedetermined based on the delay value (Δ) of the embedded buffer elementin the design as in FIG. 4. In various particular embodiments, thepredetermined amount by which D1 must be greater than D₀ is at least 5%,at least 10%, at least 20% or at least 50%. In addition, for passivewireless devices (e.g., RFID tags) that harvest energy transmitted by atransmitter device (e.g., an RFID interrogator), it is preferable thatP₀<<P₁. In various particular embodiments, the predetermined amount bywhich P1 must be greater than P₀ is at least 5%, at least 10%, at least20% or at least 50%.

In order to decode an encoded signal that was encoded using the schemejust described, a decoding signal is created by delaying the encodedsignal by a time Δ, and the encoded signal is sampled using the decodingsignal. In particular, as shown in FIG. 3, according to this samplingtechnique, the decoded binary symbol (the decoded bit) at each portionof the encoded signal (each portion corresponding to a square waveperiod) is the value (logic high or logic low) in the encoded signalthat corresponds in time to each rising edge of the decoding signal. Inthe present invention, for the decoding to function properly, D₀<Δ<D₁.Thus, in a wireless serial data transmission system that employs atransmitter device and a receiver device and that employs the pulsewidth coding scheme of the present invention, data is communicated fromthe transmitter device to the receiver device as follows: (i) a datastream in the form of a series of binary symbols (i.e., 1s and 0s) isencoded using the scheme described above to generated an encoded datasignal, (ii) the encoded data signal is transmitted from the transmitterdevice to the receiver using an appropriate modulation technique (i.e.,the encoded data signal is used to modulate a carrier), (iii) thetransmitted signal is received and demodulated at the receiver device inorder to obtain the original encoded data signal, (v) the receiverdevice creates a decoding signal from the encoded data signal as justdescribed (by delaying the encoded data signal), and (v)) the receiverdevice decodes the encoded data signal to extract/obtain the originaldata stream (the series of binary symbols) by sampling the encoded datasignal using the decoding signal.

FIG. 4 is a schematic diagram of a decoder circuit 5 according to onenon-limiting, exemplary embodiment that may be used to decode andencoded signal that was encoded using the scheme of the presentinvention. As seen in FIG. 3, decoder circuit 5 is implemented as adigital circuit, and includes a delay buffer 10 that introduces a timedelay equal to Δ, a D flip-flop 15 having D and clock (Clk) inputs and aQ output, and a storage register 20 (e.g., a shift register) that iscoupled to the Q output of D flip-flop 15. The encoded signal to bedecoded is fed to both the D input of D flip-flop 15 and the input ofdelay buffer 10. The output of delay buffer 10, which is the decodingsignal described above, is fed to the clock (Clk) input of D flip-flop15. In operation, with each rising edge of the decoding signal (createdby the delay buffer 10), the value (logic high or logic low) of theencoded signal will appear on the Q output of D flip-flop 15 as thedecoded bit output. The decoded bit output is then stored in a serialmanner in storage register 20. It should be noted that decoder circuit 5does not need a clock signal, and thus consumes less power than adecoder that requires a high frequency dock signal.

The present inventors implemented and tested an embodiment of thepresent invention (including an embodiment of decoder circuit 5) whereinP₀=P₁=25 μs, D₀=0.4 μs, D₁=20 μs, and Δ=0.5 ns. The present inventorsalso compared the performance of that embodiment to a conventionalclocked PIE decoder. Post layout power simulation results were obtainedusing Cadence Encounter using 45 nm PTM library for 1.1 V V_(DD) onLinux Platform. The post layout switching power consumption of thetested embodiment of the present invention was found to be 8.6 nW ascompared to 2234 nW for the conventional clocked PIE decoder. Thus, theswitching power consumption of the conventional clocked PIE decoder isabout 260 times greater than the decoder of the present invention.

Referring to FIG. 5A, in a further aspect of the present invention andaccording to one exemplary embodiment, a counter-less shift register 25is provided. In this exemplary embodiment, shift register 25 is providedwith n storage positions 30 (identified by the position numbers 0-6 inFIG. 5A), and shift register 25 is structured to store a fixed lengthdata word having n−1 bits. Thus, shift register 25 includes an “extra”storage position 30 that is provided at position 0 (with position 6being the most significant bit (MSB) and position 1 being the leastsignificant bit (LSB)). The function of the “extra” storage position 30at position 0 is described in detail below. In order to illustrate thepresent embodiment, in FIG. 5A, n=7 and the fixed length data word is 6(n−1) bits long. It will be understood, however, that this is meant tobe exemplary only and that other values of n may also be used.

In shift register 25, each storage position 30 may be implemented in theform of a suitable flip0flop, such that shift register 25 comprises acascade/chain of flip-flops in which the output of each flip-flop isconnected to the data input of the next flip-flop in the chain. Thiswill result in a circuit that shifts by one position the bit arraystored in it each time that a new bit is loaded into the first position.

In addition, according to an aspect of the present embodiment, shiftregister 25 is provided with a unique reset/initialization condition,shown in FIG. 5B, wherein the MSB (position 6 in FIG. 5B) is set to 1(logic high) and all other storage positions 30 (positions 0-5) are setto 0 (logic high) (i.e., the data word “1000000” is loaded into shiftregister 25). This unique reset/initialization condition thus providesthe ability to easily determine/recognize when storage register 25 isfull (i.e., has been fully loaded with the fixed length n−1 bit word)without the need for a counter simply by monitoring the state of theextra storage position 30 at position 0. In particular, afterreset/initialization, as data is added to shift register 25, if thatposition is a 0 (logic low), the storage register 25 is not full. Whenthat position becomes a 1 (logic high), the storage register 25 is full.This is illustrated in FIGS. 6A-6F, which shows the n−1 bit long dataword “D₅D₄D₃D₂D₁D₀” being sequentially loaded into shift register 25. Asseen in FIGS. 6A-6F, position 0 remains logic low until all of the n−1bits have been loaded. Counter-less shift register 25 as just describedthus removes the need for a counter to determine if and when all of thebits have been loaded into shift register 25.

According to a further embodiment, counter-less shift register 25 may beused to store variable length data, i.e., data words having differentlengths (e.g., different operations may be performed based on datalength). For example, and without limitation, counter-less shiftregister 25 may be used to store data words having lengths n−1 (6 bitsin the present example; data word “D₅D₄D₃D₂D₁D₀”) and n−2 (5 bits in thepresent example; data word “D₄D₃D₂D₁D₀”). This is illustrated in FIGS.7A and 7B. In this embodiment, part of the data word (e.g., the LSB (D₀)thereof) is used to indicate the length of the word currently beingloaded into shift register 25. For example, D₀=1 may indicate that aword having a length of n−1 is currently being loaded and D₀=0 mayindicate that a word having a length of n−2 is currently being loaded.In operation, immediately following reset/initialization as describedabove, position 6 (the first loaded position) of shift register 25 ismonitored to determine the state of D₀. That state will indicate whichone of the storage positions 30 needs to be monitored for a change from0 to 1 to indicate that the register is full. Thereafter, oncedetermined to be full, the data word can be read out of shift register25. It will be appreciated that the above is meant to be exemplary only,and that different word lengths (e.g., n−1, n−2, n−3 and n−4) and/ordifferent parts of the data word to indicate current length being loaded(e.g., D₁D₀, wherein 00=n−1, 01=n−2, 10=n−3 and 11=n−4) may also beemployed within the scope of the present invention.

FIG. 8 is a schematic diagram of an RFID system 35 according to oneparticular embodiment that employs both the low-power pulse width codingscheme and associated decoding method and apparatus described herein inconnection with FIGS. 1-4 and the counter-less shift register 25described herein in connection with FIGS. 5A-7B. As is known in the art,RFID systems consist of a number of radio frequency tags or transponders(RFID tags) and one or more radio frequency readers or interrogators(RFID readers). The RFID tags typically include an integrated circuit(IC) chip, such as a complementary metal oxide semiconductor (CMOS)chip, and an antenna connected thereto for allowing the RFID tag tocommunicate with an RFID reader over an air interface by way of RFsignals. In a typical RED system, one or more RFID readers query theRFID tags for information stored on them, which can be, for example,identification numbers, user written data, or sensed data. RFID systemshave thus been applied in many application areas to track, monitor, andmanage items as they move between physical locations. Thus, RFID system35 shown in FIG. 2 includes an RFID reader 40 and a plurality of RFIDtags 45.

FIG. 9 is a schematic diagram showing certain selectedcomponents/functionality of the RFID tags 45. In the present embodiment,RFID reader 40 is structured to transmit data to the RFID tags 45 usinga known cyclic redundant code (CRC) for detecting errors in datatransmission. Thus, for communicating information from RFID reader 40 toRFID tags 45, RFID reader 40 will generate a data frame that includes adata bit stream with a CRC bit stream appended thereto, with that dataframe being sent to the target RFID tag 45 in encoded form as describedherein (using the low-power pulse width coding scheme). As a result, asseen in FIG. 9, each REID tag 45 includes a decoding module 50 and a CRCmodule 55. The decoding module 50 is structured to receive thedemodulated version of the encoded signal that was received by RFID tag45 from REID reader 40, and decode that signal (thereby obtaining theoriginal data frame that includes the data hit stream with the CRC bitstream). The CRC module is structured to receive the decoded signal andperform the CRC error checking function on the decoded signal.

Thus, in the embodiment shown in FIG. 9, decoding module 50 includesdecoder circuit 5 as described elsewhere herein that may be used todecode an encoded signal that was encoded using the low-power pulsewidth coding scheme of the present invention. As seen in FIG. 9, thestorage register of decoder circuit 5 (labeled 20 in FIG. 4) isimplemented in the form of shift register 25 described in detail inconnection with FIGS. 5A-7B. Thus, decoding module 50 includes acomparator 60 which monitors the state of the “extra” storage positionof shift register 25 in order to determine when shift register 25 isfull as described elsewhere herein. When it is determined that shiftregister 25 is full, the data from shift register 25 (i.e., the dataframe that includes the data bit stream with the CRC bit stream) isprovided to CRC module 55 so that the appropriate CRC checking can beperformed thereon.

In the claims, any reference signs placed between parentheses shall notbe construed as limiting the claim. The word “comprising” or “including”does not exclude the presence of elements or steps other than thoselisted in a claim. In a device claim enumerating several means, severalof these means may be embodied by one and the same item of hardware. Theword “a” or “an” preceding an element does not exclude the presence of aplurality of such elements. In any device claim enumerating severalmeans, several of these means may be embodied by one and the same itemof hardware. The mere fact that certain elements are recited in mutuallydifferent dependent claims does not indicate that these elements cannotbe used in combination.

Although the invention has been described in detail for the purpose ofillustration based on what is currently considered to be the mostpractical and preferred embodiments, it is to be understood that suchdetail is solely for that purpose and that the invention is not limitedto the disclosed embodiments, but, on the contrary, is intended to covermodifications and equivalent arrangements that are within the spirit andscope of the appended claims. For example, it is to be understood thatthe present invention contemplates that, to the extent possible, one ormore features of any embodiment can be combined with one or morefeatures of any other embodiment.

What is claimed is:
 1. A method of encoding a data signal including aplurality of first symbols and a plurality of second symbols,comprising: creating an encoded signal based on the data signal, whereinin the encoded signal each of the first symbols is represented by afirst square wave having a first period P₀ and a first duty cycle D₀ andeach of the second symbols is represented by a second square wave havinga second period P₁ and a second duty cycle D₁, and wherein D₁>D₀ andP₁≧P₀.
 2. The method according to claim 1, wherein P₁>P₀.
 3. The methodaccording to claim 1, wherein D₁ is at least 10% greater than D₀.
 4. Themethod according to claim 3, wherein D₁ is at east 20% greater than D₀.5. The method according to claim 4, wherein D₁ is at least 50% greaterthan D₀.
 6. The method according to claim 1, wherein the first symbol isa logic low and the second symbol is a logic high.
 7. An RFID readerdevice that is structured to encode a data signal including a pluralityof first symbols and a plurality of second symbols by performing stepscomprising: creating an encoded signal based on the data signal, whereinin the encoded signal each of the first symbols is represented by afirst square wave having a first period Po and a first duty cycle Do andeach of the second symbols is represented by a second square wave havinga second period P1 and a second duty cycle D1, and wherein D1>Do andP1>Po.